Dredging may not eliminate contaminants 

[June 06, 2007]  WASHINGTON (AP) -- Contaminated sediments in rivers and bays from coast to coast pose an environmental hazard, and while dredging reduces the sediment, it doesn't always solve the problem, the National Research Council reported Tuesday.

Inevitably dredging leaves some contamination behind, and in some cases further treatment is necessary, such as capping with a layer of clean material, the council said.

In addition, the dredging process itself can release some contamination into the environment, said the council, an arm of the National Academy of Sciences.

The study, requested by the Environmental Protection Agency, evaluated 26 environmental dredging projects in rivers, harbors, lakes and bays across the country contaminated by industrial, agricultural and mining byproducts.

Dredging is the most complex and costly method of cleanup, the report said, but has the potential to permanently remove contaminants from the environment.

But some contamination can be left behind, particularly in places with debris such as boulders or cables, or bedrock lying beneath the contaminated sediment -- a situation for which the public may have little tolerance.

Such controversies can expand with the size of the contaminated site and the amount of work needed, notable examples being the Hudson River in New York and the Fox River in Wisconsin, the study said.

The presence or absence of such conditions should be a major consideration in deciding whether to dredge at a site, said the committee. At some sites, capping the contamination with a layer of clean material may be necessary, the report said.

The report said decisions on dredging should consider the impact of any chemicals that will be released in the process and methods to be used to minimize this release.

Following a cleanup, environmental monitoring is necessary to evaluate the success of the effort, and such monitoring was inadequate at some locations, the report said.

The EPA should improve monitoring, making sure it is done at all such sites, and the data should be available to the public.

Among the cleanup areas studied were, in alphabetical order of states:

• Alaska: Ward Cove

• California: Richmond

• Delaware: Christina River

• Illinois: Waukegan Harbor

• Louisiana: Bayou Bonfouca

• Massachusetts: New Bedford Harbor

• Michigan: Manistique Harbor

• New York: Cumberland Bay, Grasse River, Hudson River and St. Lawrence River

• Ohio: Black River

• Rhode Island: Newport Naval Complex

• Texas: Lavaca Bay

• Washington: Commencement Bay Duwanish Diagonal, Seattle; Harbor Island, Puget Sound

• Wisconsin: Fox River

The National Academy of Sciences is an independent organization chartered by Congress to advise the government on scientific matters.

On the Web:

• National Research Council: http://www.nationalacademies.org/nrc

[Text copied from Associated Press file]